Monday 16 November 2020
Otago Regional Council (ORC) staff will be out around the region sampling and testing water quality for the summer recreation season in a few weeks’ time.
Prospective swimmers in Otago are encouraged to check the ‘Can I Swim Here?’ section of the LAWA (Land Air Water Aotearoa) website to see the latest weekly water quality results from 1 December until 31 March.
General Manager Strategy, Policy and Science Gwyneth Elsum said water quality was prone to change, so it was important to confirm water is safe before swimming.
“Even the sites that typically have excellent water quality can see bacteria spike as a result of heavy rainfall washing contaminants from urban and rural land into waterways.
“That’s why we recommend people avoid swimming for 2-3 days after heavy rainfall and use the ‘Can I Swim Here?’ data to help decide if they want to swim at a particular site.”
This year, there will be new signage up at a number of popular sites directing swimmers to the information online, at www.lawa.org.nz/swim.
Potentially toxic algae (cyanobacteria) can also cause water quality concerns when there are toxic algal “blooms”. ORC recommends people learn how to identify potentially toxic algae in lakes and rivers, avoid contact with water if they suspect potentially toxic algae are present, and keep dogs on a leash and away from the water’s edge.
A general rule of thumb is that if lake water is looking green, stay out of it and avoid any contact with algal scum. For rivers, potentially toxic algae grow on rocks and can wash up along the water’s edge in mats.
To learn more about potentially toxic algae, visit https://www.lawa.org.nz/learn/factsheets/potentially-toxic-algae/
Long-term grades refreshed
Long-term grades have been refreshed on the LAWA website for the start of the swimming season. The long-term grades provide a precautionary indication of the water quality at each swimming site.
The long-term grades shown on LAWA are calculated for all sites in New Zealand using a consistent formula, based on the previous five years of data collected by regional and unitary councils during summer recreation seasons.
In Otago, six sites have ‘poor’ long-term grades, which means they have elevated bacteria concentrations 5% or more of the time. A poor grade can indicate a higher risk of illness to swimmers.
The sites in Otago with ‘poor’ long-term grades are:
The long-term grade can be influenced by samples being collected during wet weather, which makes it harder for certain sites to get “good” or “excellent” grades.
Under new national guidelines, action plans are required to be developed for all poor- graded freshwater swimming sites. ORC will identify one of the above sites as a pilot for developing action plans under the new national guidelines this year and then roll the pilot out across all the sites.
Other sites not subject to the pilot action plan will remain a focus of Council activities, such as compliance and collaborative environmental improvement aimed at improving water quality.
The sites with a “fair” grade, indicating a smaller risk to swimmers, are:
The 14 other summer recreation monitoring sites in Otago have “good” or “excellent” quality and minimal risk of infection to swimmers, or insufficient data samples for a long-term grade.
To see long-term water quality grades and the results of weekly water quality sampling (from December until the end of March), visit www.lawa.org.nz/swim.
Frequently asked questions:
Why might the long-term grade be different from the weekly testing results?
In some cases, the long-term grade for a particular swimming spot may be “poor” while the weekly testing shows that it’s OK for swimming. This can occur because the long-term data may include wet seasons, when there are high water flows and elevated bacteria from runoff.
Water quality results are variable from year to year; when summer is wet, rivers are generally higher and bacteria results poorer. A long, hot summer generally bodes well for water quality. That is why it is recommended that even for sites with generally good water quality, swimming is avoided for 2 - 3 days after heavy rainfall, as urban or agricultural runoff can affect bathing water quality.
However, in some areas a long, hot summer can lead to increased potentially toxic algal blooms in our rivers and lakes, so it is important to get familiar with what these looks like so you can avoid them.
The best indicator of whether it’s safe to swim at your local swimming site is to use the recent weekly sampling results during the Otago summer recreation season of 1 December to 31 March.
Getting familiar with the general history of the water quality results as a site, and using common sense (does the water look clean and clear? has it been raining recently? are there any nearby sources of pollution?) are a useful rule of thumb before deciding where and when to swim.
What is ORC’s role in summer recreation monitoring?
ORC is required to monitor water quality during the contact recreation period (1 December until 31 March in Otago) and has been doing so for many years.
At some sites, ORC undertakes Faecal Source Tracking (FST) to identify the source of bacteria when there is a spike.
What is ORC doing to address the sites with a poor long-term grade?
Under new national guidelines, action plans are required to be developed for all poor-graded swimming sites. This year, ORC will identify one of the poor sites as a pilot for developing action plans.
How do I know if the water is safe for swimming?
Generally, if the most recent results on the LAWA website show the water quality meets the swimming guidelines, the water looks clean and clear, and it hasn't been recent heavy rainfall since the last sample date, then it is likely that the water quality will be safe for swimming.
What causes water quality to be poor?
Heavy rain tends to wash contaminants off land and into waterways, which causes bacteria spikes when we test the water quality. We also know that in some of Otago’s lakes, for example Lake Hayes, the water quality is excellent out from the shore but faecal contamination around the shoreline is likely to be due to ducks.
What’s the best way to find out if it’s safe to swim?
Head to the “Can I Swim Here?” section on the LAWA website, which shows weekly water quality testing results for not only Otago but all of NZ, so you can check out the water quality wherever you’re holidaying this summer: https://www.lawa.org.nz/swim.